Gating system for cathode-ray oscilloscopes



J. R. MOORE GATING SYSTEM FOR CATHODE-RAY OSCILLOSCOPES 2v SHEETS-SHEET2 Filed Nov. 28, 1942 Ow Om K s mw .JAMES R. M RE ATTORNEY Patented Mar.31, 1953 GATING SYSTEM FOR CATHODE-RAY OSCILLOSCPES James R. Moore,Rumson, N. J., assignor to the United States of America as representedby the Secretary of War Application November 28, 1942, Serial No.467,267

(Granted under Title 35, U. S. Code (1952),

sec. 266) Claims.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes, without the payment to me ofany royalty thereon.

This invention relates to cathode ray oscilloscopes in general, and alsoto such oscilloscopes used in pulse echo systems for locating andranging.

The primary object of my invention is to generally improve cathode rayoscilloscope circuits. Another object is to generally improve pulse echosystems.

Pulse echo systems for locating and ranging comm-only employ a cathoderay oscilloscope to show the echo peak. Reception is comp-licated by thelocally transmitted radio pulse, and by the reception of numerous echopeaks from objects other than the one in which the operator isinterested. There is also the common appearance of so-called grass alongthe base line of the oscilloscope, all adding to the dilculty andconfusion of the operator.

One object of my invention is to overcome the foregoing difficulties byso controlling the signal transducer, in this case a cathode-rayoscilloscope, at the receiver, that it will discriminate in favor of adesired echo. This is done by normally maintaining the transducerinoperative and then rendering it operative during time of reception ofthe desired echo.

Another object of my invention is to overcome the foregoing difficultiesand to blanket the oscilloscope at points along the base line other thanat the echo peak of interest. In effect the oscilloscope is gated topresent the echo response at only one part of the base line, and theresponse at all other parts of the base line is blanketed. This is doneby applying a gate wave or bias wave to a control electrode in theoscilloscope, said gate wave having a relatively long negative portionadapted to cut olf the electrode beam, and having a relatively shortpositive or gate portion adapted to pass the electron beam at one partof the base line.

A further object of my invention is to insure maintenance of propersynchronism between the gate wave and the sweep wave, and with thisobject in View I derive both the gate wave and the sweep wave from asingle sine wave source. It is usual to provide a phase changer to shiftthe sweep or base line on the oscilloscope screen. This may be done tocenter a desired echo peak, or it may be done for ranging. In accordancewith a further feature and object of my invention the 'phase changingmeans is located between the sine wave generator and both the sweep waveand Another object of my invention is to make it possible to shift thelocation of the gate relative to the base line, thus making it possibleto select which of a number of echo peaks is to be presented forobservation and tracking For this purpose I provide an additional phaseshifting mechanism between the aforesaid phase changer and the gate wavegenerator, the second phase shifter being operable independently of therst, and controlling only that portion of the sine wave energy which isfed to the gate wave generator.

It is desirable to be able to control not only the location of the gatealong the base line, but also the width of the gate, and a furtherobject of my invention is to provide suitable apparatus for thatpurpose, said apparatus preferably being associated with and forming apart of the gate wave generator or beam modulator.

While I have so far referred to my invention as applied to pulse echosystems, it will be understood that the provision of a gate ofcontrollable width and controllable location on the screen of anoscilloscope is of general application to many Oscilloscopes used forpurposes other than pulse echo systems, and the invention is accordinglynot intended to be limited to the latter.

To the accomplishment of the foregoing general objects and other morespecific objects which will hereinafter appear, my invention resides inthe method and apparatus elements and their relation one to the other asare hereinafter described in greater detail in the followingspecii'ication. The specification is accompanied by a drawing in whichFigure 1 is explanatory of the purpose of my invention;

Figure 2 schematically illustrates the effect of gate width control;

Figure 3 schematically illustrates the effect of the independent phaseshifter for the gate wave;

Figure 4 is a schematic diagram in block form showing how the inventionmay be applied to a typical pulse echo system for locating and ranglng;

Figure 5 is a wiring diagram showing one form of the gate wave generatorwith gate width control; and

Figure 6 illustrates a modified form of gate wave generator withassociated phase shifter.

Referring to the drawings, and more particularly to Figure 1, I thereshow a typical screen trace found in the operation of a pulse echosystem. The transmitter pulse produces a tall lpeak I2. Three main echopeaks are shown at le, I6 and i8. These correspond to reilection of thetransmitted radio wave from different objects, typically airplanes. Inaddition, there are nu-r merous smaller peaks along the b ase line,commonly referred to as grass Sometimes the trace is confusing and it isdifficult for the operator to distinguish a desired echo peak fromotherecho peaks and from the grass. In accordance. with the presentinvention, the response of the oscilloscope is wiped out or blanketed atall points except between limits indicated' by the broken lines and 22.rShese constitute a so calledgate or aperture through which the responsepattern of the oscilloscope is admitted.- rvhe remain-ing, peaks are allshown in broken lines to indicate that they are not visible. Peak le atthe gate is shownin solidlines to indicate that thisportion is? visible.It will be evident that theV task of traclfring;l a particular object isgreatly facilitated when only its echo peak is exposed on the screensurface.

Some form of gate width control is desirable, the-purpose of this beingschematically illustrated in Figure' 2. A single tooth of the sweep waveis shown at 2d. The-positive pulse of the gate wave is shown at 25. Itwill be clear that for some purposes a narrow gate may be needed, asshown at 2Q, while in other instances a wider gate may be needed, asshown at 23. and 2,8.

It is also evident that the location of the gate along the base lineshould be variable, and this is schematically illustrated in Figure 3. Asingle tooth of the sweep wave is shown at 32, while the positive pulseof the gate wave may be shifted relative toV the sweep wave, asA shownby the successive positions 3Q, 35 and 38.

Referring now to the block diagram of Figure 4, a directional antennatransmitting array is indicated at 40. This is supplied by transmitter42'; the carrier wave of which is pulsed or modulated by modulator M.The keying or pulse frequency is determined by a sine wave generator 45,the output of which is transformed to pulses by means of a pulsegenerator 48.

Al portion of the sine wave energy from gener-v ator-46 is used tosynchronously-control the sweep of the Oscilloscopes. In the presentcase there are three Oscilloscopes, a ranging oscilloscope 50,

oscilloscope 52 for elevation tracking, and oscille-- scope 54 forazimuth tracking. For this purpose the sine wave is supplied to a sweepwave generator 56, typically a Saw tooth wave generator'. The reflectedor echo energy is collected on a plurality of directional antenna arraysEl), 62 and 64, which in turn are respectively connected to receiverslll, l2 and l. These are used respectively for ranging, elevationtracking, and azimuth tracking, and it will be understood that theoutputs of the receivers are applied to deflection plates of theOscilloscopes 50, 52 and 54 in conventional fashion. For example, ifVthe sweep potential is applied to horizontally deecting plates of theOscilloscopes, the echo peak'Y potentials are applied to verticallydeflecting plates. A trace such as that shown in Figure l will tend tobe produced on all three Oscilloscopes. A phase changer 'i6 is disposedbetween sine wave generator 46 and sweep wave generator 56. This phasechanger may be used to shift the base line on the screenvof theoscilloscope, thus locating or-centering the echo peaks. Thephasechang'er may also be used for ranging by measuring the preciseamount of change needed to shift from the transmitted peak I2 (Figure 1)to the echo peak I6, relative to a center line on the oscilloscopescreen.

In accordance with the present invention, a portion of the energy fromthe sine wave generator A6 is supplied to a beam modulator 18, Thiscomprises what may be termed a gate wave generator 80. The gate wavegenerator derives from the sine wave a synchronous wave which issubstantially rectangular and which comprises4 a; relatively longnegative portion and a relatively short positive gate portion. The gate1 wave is applied to a`- control electrode 82 in oscilto originallyprovide the; proper adjustment. I.

provide a. variableA phase shifter in the beam: modulator '18. thatportion, of4 the sine Wave. energy whichl is supplied to the gate wavegenerator, andV there forev shifts the gate pulserelative toi the sweep,The amount ofl phase;

wave and base line. shift introduced by phaseishifter 86inorder to makethe gate pulse coincide with a selected echo. peak will also beYindicative of the range-tc the. object from which the echo isgreilected.Thisthev shift illustrated in Figure 3 of the drawing,`

ItV will be noted thatthe point 88 at which the.A

sine wave energy-is tapped for feed, to the beam modulator 'i8 followsthe phase shifter 16. This is important because in the event of anyInove-A ment of phase shifter l5 causing movement along-l the base linecf the transmitter andbase line, the gate is automatically movedwithre,-

spect to the baseline, thus remainingy in proper.-

relation` to thefselected echoi peak; Since move;- ment; of echo peaksmaybe dueto changeY in4 ac-f tualrange or setting' ofi phase changer;the gate.-

may be said to present whatever"v is selected atzcr` near the centerline of 'the rangeoscilloscope One specific form of gate wave generator;circuit is illustrated in Figure- 5 of theA drawing.. Referring to thisligure;A the sine wave energyV is supplied at the point 90, and isappliedto; the

control electrode of an amplifier tube` 92, the.

output of which is supplied thrusuitable resiste ance coupling toanotherfamplier tube' 94:. The latter tube is selected to saturate atthe potential:`

applied thereto, causing iti to swing beyond the kneeof thecharacteristic: curve of 'the' tube when. The tube is so biased'.thatthe negative: swing of the grid goes beyond; thefcut off' point ofthe tube. Asl a' result the.

the grid swings positive.

wave is flattened at the top and the bottom', producing anapproximately. square wave.. The

slope: of thev sides of the wave is very steep: if

the amplitude of the applied wave isverymu'ch larger than that oftheoutputwave, buts at .an

angle (less steep) if the amplituder ofthe appliedwave. is. onlymoderately largerthan that' of the. output wave.

to aapulse wave by the useof inductance coupling'.

shown at 96. The tube 98 thus acts as apulse generator, the output ofwhich is supplied to 'apower'amplier: tubey |00, Which;..ampli'es. thelThis phase shifter affects only.1

The output wave is then changedA pulse to the necessary magnitude forapplication to the control grid of the oscilloscope.

The magnitude of the sine wave applied to the gate wave generator iscontrolled by means of a potentiometer |02. This control varies thearnplitude of the sine wave relative to the limited or flattened outputwave of the tube 94, and so determines the slope of the sides of theflattened output wave.

This in turn determines the sharpness or Width of the pulse derived bythe di La method referred to heretofore. In this way the potentiometer|02 acts as a gate Width control, producing the effect illustrated inFigure 2 of the drawing. It will be noted that, although gating pulses20, 28 and 30 in Figure 2 differ in width, their mean time ofoccurrence, and therefore the mean spacing between successive gatingpulses is kept substantially constant.

It will be understood that the gate Wave generator shown in Figure 5corresponds to the block B0 in the block diagram of Figure 4. The phaseshifter shown at 86 in Figure 4 may be of any conventional type, such asthat using Helmholtz coils.

In one aspect, it may be said that the control electrode is normallybiased negatively to cut off the electron beam, and that an intermittentpositive pulse overcomes the bias. The block diagram of Figure 4 doesnot show details such as biasing means, but these are, of course,employed. From this standpoint the term gate wave may be considered asmeaning the sum of the steady bias and the pulse. The resultant waveordinarily has a relatively long negative portion and a relatively shortpositive portion.

Figure 6 illustrates another form of beam modulator, that is, phaseshifter and gate wave generator. Referring to that gure the sine waveinput at |04 is applied to the top and bottom corners of an RC bridgemade up of resistors |06 and |08 and condensers H0 and H2. One end ofeach potentiometer resistor H4 and H is connected to each of one pair ofconjugate terminals of the bridge and the other end of eachpotentiometer resistor is selectively connected through a polarityreversing switch, such as a double pole double throw switch withtransposition connectors to permit the desired operation, to each of theother pair of conjugate terminals of the bridge, as shown.

Assuming that the poles of the switch H8 are thrown to the right, thepotentiometer ||i is connected in shunt around the condenser H0, and thepotentiometer I I6 is connected in shunt around the condenser l2. Themovable contacts |20 and |22 of the potentiometers are mechanicallyconnected for simultaneous movement. (For example, with a rotatingcontrol they may be arranged on a common shaft.) This mechanicalconnection is schematically illustrated by the broken line connection|24 on the diagram. It will be evident that when contacts |20 and |22are moved all the way to the right, the output is being taken at theleft and right corners of the bridge, resulting in a substantial phaseshift relative to the phase at the top and bottom corners of the bridge.As the contacts are moved back in opposite directions the effect of thecapacitative phase shift is lessened, until finally when contacts |20and |22 are moved all the Way to the left, there is no change in phaseat all, the connections being to the top and bottom of the bridge. Bythrowing the switch H8 to the left, the potentiometers are connected inshunt with the resistors of the bridge, instead cf the condensers, thusproviding a further range of phase shift.

The sine wave output from the phase shifting bridge is applied to a tube|30 which ampliiies the sine wave and feeds the same through transformer|32 to a. tube |34 selected to saturate at the top of the wave andbiased to cut off at the bottom of the wave. The output of tube |3i is aflattened Wave, which is converted to a pulse wave by means of an RCcircuit comprising a condenser |35 and a resistance |38. The sharpnessor width of the pulse depends on the time constant of the RC circuitrelative to the frequency of the sine Wave. This may be varied by makingeither the condenser |36 or resistor |38, or both, variable as shown.This produces the desired gate width control shown in Figure 2.

The pulse wave or gate Wave is amplified by an amplifier tube |50, theoutput of which is supplied to the control electrode of theoscilloscope.

It should be understood that While I have shown simple triodes in thewiring diagrams of Figures 5 and 6, in actual practice the tubes willordinarily be pentode tubes or other multiple electrode tubes havinggreater eiciency for Work with high frequencies of the order herecontemplated.

It is believed that the construction and operation of my improved gatesystem for cathode ray Oscilloscopes, as well as the many advantagesthereof, will be apparent from the foregoing detailed description. Itwill be understood that the use of a gate or aperture of variable widthand variable location on the oscilloscope screen is valuable in fieldsother than pulse echo systems. The invention is of particular value inconnection with pulse echo systems, and is illustrated as applied tosuch systems for that reason, and also by Way of exemplication of theinvention, but not in limitation thereof.

It will therefore be apparent that While I have shown and described myinvention in several preferred forms, many changes and modifications maybe made without departing from the spirit of the invention, as sought tobe defined in the following claims. In some of the claims I refer to thegate being located at a desired echo peak, but this is not intended toexclude the illumination of two or more peaks Where desired. Forexample, in locating objects by so called double tracking," twoimmediately adjacent and preferably overlapping or slightly spread echopeaks are simultaneously visible for comparison with one another. Thegate is located at this slightly spread pair of peaks.

I claim:

1. In the operation of an oscilloscope having a control grid, the methodof presenting only a desired portion of the trace while excluding allother response, which includes generating a sine Wave, deforming a.portion of the sine wave energy into a sweep wave for the oscilloscope,deriving a relatively rectangular bias potential wave from a portion ofthe aforesaid sine wave energy, said bias potential wave having arelatively long portion adapted to cut )off the electron beam and soblanket the oscilloscope, and having a relatively short gate portionadapted to pass the electron beam at one point along the base line whileblanketing the same at other points along the base. line; applying'said. gate.r wave.- to a. control. grid in the oscilloscope, wherebychange in phase oi the; sine wave with. consequentA shi-ft in the baseline of the oscilloscope trace is accompani'ed by a corresponding shiftlin` the location of the gate portion of the gate wave-l and inde-ypendently shifting thev phase: of that.- portion of the` sine. wave usedfor generating the` gate waveV when it.l is desired. to shift'- the^location of. the'. gate'. relative to the-.base line in'. order to'properly locate the. gate at a4 desired. point;

2. En the'- location of: objects by means: of a. pulse echo` systemhaving ari. oscilloscope to; showthe echo peaka the. method oi:ypresenting onlya desired echoy peak; whileA excluding.' all otherresponse, wlfiiclil includes. generating an. approximate sine wave,deformingia portion of the sine WaveI energy intoy asawf tooth'. sweepwave for' the oscilloscope, deriving a'v relatively rectarigu.'- lar'biasl potential wave from. a. portion. of. the'- aforesaid sinz-:vwavevenergy, said` bias. potential'. wave having a. relatively long negativeportion adapted to-v out off' the electron. beam. and. so. blanket theoscilloscope, and: havingv a. relatively short positive gate portionadapted to pass the. electron beam at one part. of: the baseline whileblanketing. the. same at.'- other parts: of.' the. base. line, applyingsaid gate. wave'. to a control. grid. in the oscilloscope', wherebychange'. in phase of' the sine wave. with consequent. shift inthe baseline and. echo peaks is accompanied. by' a` corre-A sponding shift inthe location of the gate. portion of the gate: wave-5. and independentlyphase shifting.' the. portion oi the sine wave' used. for. generatingthe` gatev wave.v when it is. desired to shift thez locationof'. thegate relative to the' base line in order' tov properly locate. the;gate. at a: de* sired` echo: peak..

3.' In combination,.. an' oscilloscope; having sweep electrodes) and' acontrol electrode. an approxi-- mate. sine wave. generator; aisweep wavegenera:- tor' deriving" a. sweep: wave: from. a, portion; oi the; sine.waveienergy',. connections applying the sweep' wave; to' thesweep-electrodes of' the oscilloscopi-i; a gate wave.. generator' for:derivinga biasorrgate' wave. from'. another portion of the aforesaid.sine wave: energy, connections applying. said-gate wave.' to` the.control. grid; of: the oscilloscope', said gate-A wavef. having.' arelatively long portion. adapted toi' cut: on! the; electron. beam and.so' blanket. the. osA cillosc'ope, and havingiarelatively'short.gatepore tion'-` adapted to;- piass the.- electron beamati'one'. point. along the base line:V while blanketing same at'. otherpoints; along the base-line, and. a'. phase changer disposed: betweenthe aforesaid sine wavev generator'and the; sweep and gatewave.ygenerators. for shifting the baseline of. the: os.- clloscope togethervwith. the gate portion. of.. the gate wave..

4. In combination,.an-.oscilloscope having sweep' electrodes and acontrol electrode, anapproximate sine wave generator,` ai sweep wavegenerator deriving a. sweep wavefrom. a portionof: the. sinewave-energyconnections applying thesweepA wave to the sweep` electrodesof the. oscilloscope;. a gate wave generator for? deriving a. bias. orgate. wave from another' por-tion of the. aforesaid sine' Waveenergyconnectionsiapplying said gate-wave. tothe control gridfof:lthefoscilloscope,1 said gateware having a. portion' adaptedvto cutoffthe electron-beam a11dv so'lblanket the-oscilloscopeE andhaving a. gate,portion.L adapted. to passi the elec.- tron beam. at. one. part: of. thebase. line while' blanlreting the. sanieat. other parts; of. the. base.line,A a phase. changendisposed between; the. aforo-v said sine wavegenerator and the sweepand gate..

wave generatorsl forV shifting the'base line ofthe oscilloscope togetherwith the gate. portion of. the

gate wave, and an independent. phase. shifter di'sposed between. theaforesaid. phase changer and..

the sweep wave to the sweep electrodes. of

the oscilloscope, a gate wave generator for deriving a. bias' or gate'.wave from another portion. of the aforesaid sine. wave energy; con-Anections applying' said. gate wavel to` the control grid of theo'scilloscopa said gate wave hav'- ing a portion adapted'. to' cut o'ithe' electron beam and so blanket the` oscilloscope, and having a gateportion adapted. to pass. the electron beam. at. one point' along: the.base line while blanketi'ng the same. at other points. along the baseline,A a phase changer disposed' between the' afcresaidsine wavegenerator and the sweep and gate wave generators for shifting' the baseline of the oscilloscopey together with the gate por'- tion' of' thegate wave,4 and gate. width control mechanism associated. with said gatewave gen-- erat'or' for determining the width. of the gate.,

61 in combinatioman oscilloscope having sweep` electrodes andV a controlelectrode,l an` approxi` mate sine wave generaton. a-sweep wave generator derivingv a sweep wave'irom a portion ofthesine wave energy;connections applying the sweep` wave' to the sweep electrodes ofthe.oscilloscope,Y a' gate' WaveV generator for deriving. a bias. or gatewave from another portion of' the aforesaid` sine wave energy,connections applying said gatewave. to the control gridv of theoscilloscope, sai'cl` gate wave'. having a portion. adapted to cut oif.vthe electron beam and. so blanket the oscilloscope.. and. having agateportion. adaptedv to pass the electron beam at one point. along the.basey line. while' blanketing the same at. other' points along? the'base line,l a phase. changer disposed. betweeny the aforesaid. sine wavegenerator and the. sweep'` andA gate Wave generators for.shiftingthe-baseline of.` the oscilloscope together wththe gate portion.of. the gate. wave, an independentr phase shifter. disposed. between.theV aforesaid phase changer and the gate wave. generator. in order tovinde-- pendently shift the location of; the; gate relative to. the base.li'neso asI tolocatethe. gate ata deV sired point,. and gate. widthcontrol mechanism associated wi'thsaid gatefwavegenerator fordeterminingthewidth of thegate.v

7i.. Apparatus for locating objects.- by' means. of. pulse. echo,- said.apparatus comprising.- a` transmitten. a. receiver, an oscilloscopehaving sweep electrodes; deflecting electrodes,E and.'v a controlfelectrode;y connections to.- feedl the receiver. output to thedeflecting electrodes, anapproximate: sineI wave generator; aY pulsegenerator.' deriving. a pulse. from a. portion' of: saidv sine: wavevenergy; a. keyer driven' by' the pulse; generator' for keying'. the:transmitten. asweep: wave generator for. de-

, riving; a sweep wave: from aA portiony off thelsin'e' wave; energy,connections. applying.' the sweepl Wave to the. sweepv electrodes@ ofthe; oscilloscope', a: gate wave. generator.' for.' deriving a. bias orgate wave. from another: portion oi; the! aforesaid sine'vwaveenereyi-connectlonsiapplymgsaidgatewave to the control grid of theoscilloscope, said gate wave having a relatively long portion adapted tocut ol the electron beam and so blanket the oscilloscope, and having arelatively short gate portion adapted to pass the electron beam at onepart of the base line while blanketing the same at other parts of thebase line, a phase changer disposed between the aforesaid sine wavegenerator and the sweep and gate Wave generators for shifting the baseline of the oscilloscope and the echo peaks thereon together with thegate portion of the gate Wave.

8. Apparatus for locating objects by means of pulse echo, said apparatuscomprising a transmitter, a receiver, an oscilloscope having sweepelectrodes, deflecting electrodes, and a control electrode, connectionsto feed the receiver output to the deflecting electrodes, an approximatesine Wave generator, a pulse generator deriving a pulse from a portionof said sine Wave energy, a keyer driven by the pulse generator forkeying the transmitter, a sweep wave generator for deriving a sweep wavefrom a portion of the sine wave energy, connections applying the sweepwave to the sweep electrodes of the oscilloscope, a gate wave generatorfor deriving a bias or gate wave from another portion of the aforesaidsine wave energy, connections applying said gate Wave to the controlgrid of the oscilloscope, said gate Wave having a portion adapted to cutoi the electron beam and so blanket the oscilloscope, and having a gateportion adapted to pass the electron beam at one part of the base linewhile blanketing the same at other parts of the base line, a phasechanger disposed between the aforesaid sine wave generator and the sweepand gate wave generators for shifting the base line of the oscilloscopeand the echo peaks thereon together with the gate portion of the gatewave, and an independent phase shifter disposed between the aforesaidphase changer and the gate wave generator in order to independentlyshift the location of the gate relative to the base line so -as toproperl locate the gate at a desired echo peak.

9. Apparatus for locating objects by means of pulse echo, said apparatuscomprising a transmitter, a receiver, an oscilloscope having sweepelectrodes, deflecting electrodes, and a control electrode, connectionsto feed the receiver output to the deflecting electrodes, an approximatesine wave generator, a pulse generator deriving a pulse from a portionof said sine Wave energy. a keyer driven by the pulse generator forkeying the transmitter, a sweep Wave generator for deriving a sweep wavefrom a portion of the sine wave energy, connections applying the sweepwave to the sweep electrodes of the oscilloscope, a gate wave generatorfor deriving a bias or gate wave from another portion of the aforesaidsine wave energy, connections applying said gate wave to the controlgrid of the oscilloscope, said gate Wave having a portion adapted to cutoff the electron beam and so blanket the oscilloscope, and having a gateportion adapted to pass the electron beam at one part of the base line,a phase changer disposed between the aforesaid sine wave generator andthe sweep wave generator for shifting the base line of the oscilloscopewith respect to the echo peaks thereon and the gate portion of the gatewave, a phase changer disposed between the sine wave generator and thegate Wave generator to selectively shift the location of the gaterelative to the base line to locate the gate at a desired echo peak andgate width control mechanism associated with said gate wave generatorfor determining the width of the gate.

10. Apparatus for locating objects by means of pulse echo, saidapparatus comprising a transmitter, a receiver, an oscilloscope, havingsweep electrodes, defiecting electrodes, and a control electrode,connections to feed the receiver output to the deflecting electrodes, anapproximate sine wave generator, a pulse generator deriving a pulse froma portion of said sine wave energy, a keyerl driven by the pulsegenerator for keying the transmitter, a sweep wave generator forderiving a sweep wave from a portion of the sine wave energy,connections applying the sweep Wave to the sweep electrodes of theoscilloscope, a gate w-ave generator for deriving a bias or gate wavefrom another portion of the aforesaid sine wave energy, connectionsapplying said gate wave to the control grid of the oscilloscope, saidgate wave having a relatively long portion adapted to cut off theelectron beam and so blanket the oscilloscope, and having a relativelyshort gate portion adapted to pass the electron beam at one part of thebase line, a phase changer disposed between the aforesaid sine wavegenerator and the sweep wave generator for shifting the base line of theoscilloscope with respect to the echo peaks thereon and the gate portionof the gate wave, an independent phase shifter disposed between theaforesaid sine wave generator and the gate Wave generator in order toindependently shift the location of the gate relative to the base lineso as to properly locate the gate at a desired echo peak, and gate widthcontrol mechanism associated with said gate wave generator fordetermining the width of the gate.

JAMES R. MOORE.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,189,549 Hershberger Feb. 6,1940 2,280,524 Hansen Apr. 21, 1942 2,405,238 Seeley Aug. 6, 19462,405,239 Seeley Aug. 6, 1946 2,406,316 Blumlein Aug. 27, 1946 2,411,572Hershberger Nov. 26, 1946 2,416,088 Deerhake Feb. 18, 1947 2,416,089Jones Feb. 18, 1947 2,417,136 Smith Mar. 11, 1947 2,453,970 CharrierNov. 16, 1948 2,470,464 Bowie May 17, 1949 2,534,862 Fox Dec. 19, 1950

